A video and lighting control synchronizing system and method

ABSTRACT

Described is a means for synchronizing the playback of video and lighting data, specifically to a method for conforming the timing of DMX 512 lighting data so as to coincide with video data.

RELATED APPLICATION

This application claims priority of

-   -   PCT/US2014/61437 filed on 21 Oct. 2014; and 61/893,788        provisional application filed on 21 Oct. 2013.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to means for synchronizing theplayback of video and lighting data, specifically to a method forconforming the timing of lighting data so as to coincide with videodata.

BACKGROUND OF THE INVENTION

It is common in entertainment and theatrical events to use both lightingand video displays in a coordinated manner in order to present a showand to improve the experience for the audience. Video images may beprovided by sources such as cameras, DVD players, media servers, harddisk recorders, computers and other similar devices. These sources maybe combined and manipulated through video switchers before being outputto display devices such as LED video screens, video projectors and othersimilar devices. The communication from the video output devices to thevideo displays may be through one of the standard video industryprotocols including, but not limited to; DVI, SDI, HD-SDI, RGB, RGBHV,VGA, SVGA.

Lighting control at the same entertainment event may be provided bylighting controllers and may communicate with lighting equipment such asdimmer racks, automated lighting, LED lighting, and other lightingdevices through a standard lighting industry protocol including, but notlimited to; DMX-512, ACN, RDM, Art-Net.

A common feature of both video and lighting communication systems isthat they are commonly frame based where data is sent based on arepeating time interval related to a portion of the signal or a physicalcharacteristic of the device. For example, with video devices a frame ofvideo relates directly to a physical frame of film in prior arttechnology. That is, a single static image. To achieve the illusion of amoving image multiple single static images are displayed one after theother and the human eye and brain will merge these such that we perceivea moving image. This effect is often referred to aspersistence-of-vision. Depending on the format being used, single imagesmay be shown at many different rates including 24 images per second, 25per second, 30 per second and so on. The rate of displaying these staticimages is often called the frame rate of the video data. The most commonframe rates used in North America are rates of 24 fps (frames persecond), 30 fps, and 29.97 fps. In other areas of the world 25 fps mayalso commonly be used. Higher frame rates such as 48 fps and 60 fps arealso utilized.

Similarly, lighting control is also often sent in a repeating mannerwith frames of data that are updated on a regular repeating basis. Thisallows lighting levels to be sent repeatedly with a different set ofstatic levels in each lighting data frame so as to give the appearanceof smooth fades or changes in lighting level. The same brain-eyepersistence-of-vision phenomenon that provides this illusion in videoalso applies to lighting so similar data frame rates are used to obtainthe smooth results desired. For example, the most common lighting dataprotocol in use for entertainment lighting control is USITT DMX-512A.This can support a maximum frame rate of 43 fps when 512 data values arebeing transmitted in each frame. In practice, many lighting controllersoperate at lower data frame rates, perhaps close to the same 30 fps asis used for video.

As mentioned earlier, both video and lighting are typically used at thesame time in entertainment and theatrical events. With the advent ofincreasing use of LED light sources both in luminaires and in videodisplay systems the timing of these devices has become even morecritical. In particular, LED and other solid state lighting devices haveessentially zero rise and decay time. This is in contrast toincandescent light sources which exhibit significant rise and decaytimes as the physical filament heats and cools. The rapid rise and decaytimes of solid state lighting can make them appear to flicker and makesthem susceptible to aliasing and interference effects, particularly whenviewed by a frame based video camera. Different frame rates in the videoand lighting systems can cause strobing, flashing and other interferenceeffects on video systems when the video and lighting frames are out ofsync or out of phase with each other. These problems may occur during,and be related to, frame by frame transitions in lighting level as wellas to static levels. Prior art systems suffered from similar aliasing orphasing problems when using high intensity discharge, fluorescent, orarc lamps with film or television cameras. A solution commonly utilizedin that prior art was to synchronize, or genlock, the phase of the mainssupply used for the luminaires and the video frame rate. This ensuredthat the light output from the lamp was always active at the same pointswithin the video frame. More recently pulse width modulated (PWM)signals used to dim LED luminaires have caused similar problems withphase aliasing on camera. These particular issues have been solved invarious manners including using very high frame rates for PWM data.However, there is currently no solution for such synchronization oraliasing problems when they are caused by the competing frame rates oflighting control data and video data.

It would be advantageous to have a method of synchronizing the framerates of lighting control data and video data in order to avoid andalleviate unwanted aliasing and interference between them.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which likereference numerals indicate like features and wherein:

FIG. 1 illustrates a schematic diagram of an embodiment of inventionsynchronizing system;

FIG. 2 illustrates a timing diagram of a first embodiment of thesynchronizing system;

FIG. 3 illustrates a timing diagram of a second embodiment of thesynchronizing system;

FIG. 4 illustrates a timing diagram of a third embodiment of thesynchronizing system; and

FIG. 5 illustrates a timing diagram of a fourth embodiment of thesynchronizing system.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in theFIGUREs, like numerals being used to refer to like and correspondingparts of the various drawings.

The present invention generally relates to means for synchronizing theplayback of video and lighting data, specifically to a method forconforming the timing of lighting data so as to coincide with videodata.

FIG. 1 illustrates a schematic diagram of an embodiment of theinvention. Lighting control system 4 is sending DMX-512 control data 6to lighting equipment 2 through a synchronizer 10. Similarly, videocontrol system 5 is sending video data 7 to video display device 3.Synchronization signal 8 connects video control system 5 to synchronizer10 so as to enable the synchronization of the lighting control data tothe video data. In operation it is desirable to utilize the video signalframe rate as the master frame rate and to synchronize the lighting datato the video, rather than the other way round. Video data frames arecritically timed and that timing should remain intact. Lighting data isalso critically timed, however, it is possible through in thisembodiment to adjust that timing and still produce a satisfactoryresult. Various embodiments are now discussed to achieve thatsynchronization and timing. All discussed example embodiments use agenlock, or frame synchronization signal, from the video data and theinvention conforms the timing of a DMX-512 lighting data signal to thatgenlock signal. However, the invention is not so limited and other typesof synchronization signal and formats of video data signal and lightingdata signal may be used without departing from the scope of theinvention.

FIG. 2 illustrates the timing diagram of an embodiment of the invention.The top timing trace 12 shows the genlock pulses 18 derived from a videosignal and provided by the video system. The provision of genlocksynchronization signals by video equipment is common as the same signalcan be used to synchronize multiple components of video systems. Aspreviously discussed, these genlock pulses may be at a 30 fps framerate, or any other frame rate as being used by the video system. Eachpulse 18 a-18 g relates to the start of a frame of the video signal. Thecenter timing trace 14 shows the raw DMX 512 lighting data frames asgenerated by the lighting control desk and input to the synchronizer. Inthe example illustrated the input DMX 512 frame rate is higher than thatof the video genlock signal, thus there are more DMX 512 frames thanvideo frames. In order to constrain the lighting DMX 512 data to theframe rate of the video genlock signal the number of DMX 512 frames hasto be reduced in some manner.

In the embodiment illustrated in FIG. 2 this data reduction is achievedby discarding some of the DMX 512 data frames and delaying others. Asillustrated frame 1 of the DMX 512 data 14 is passed through ascoinciding with the first pulse 18 a of genlock signal 12. The DMX 512data now passes into a buffer within the synchronizer of the invention.This buffer accumulates a single pending DMX 512 data frame and awaitsthe arrival of the next genlock pulse 18 before releasing that frame.Thus, frame 2 is accumulated in the buffer and is output on receipt ofthe next genlock pulse 18 b. DMX 512 frame 3 is next accumulated withinthe buffer, however DMX 512 frame 4 arrives before the next genlockpulse 18 c is seen. Thus, the buffer discards frame 3 and instead,accumulates frame 4. Frame 4 is then output on receipt of the nextgenlock pulse 18 c. The system proceeds in this manner and outputs DMX512 frames 1, 2, 4, 6, 8, 9, and 11 synchronized with genlock pulses 18a-18 g. DMX 512 frames 3, 5, 7, and, 10 are discarded.

The situation illustrated in FIG. 2 where the DMX 512 frame rate isgreater than that of the video genlock signal is the more common inpractice, however, if instead the DMX 512 frame rate was lower than thatof the video genlock signal, the invention is still operative. Underthese conditions, the DMX 512 frames may be repeated from the bufferwithin the synchronizer in order to create the necessary extra DMX 512data frames.

FIG. 3 illustrates a timing diagram of a second embodiment of theinvention. The timing diagram presents the same situation as FIG. 1where the DMX 512 frame rate is greater than that of the video genlocksignal. In this embodiment the data reduction is achieved through thecombination and interpolation of DMX 512 data frames instead ofdiscarding frames. The process is similar to that described in FIG. 2.As illustrated in FIG. 3, frame 1 of the DMX 512 data 14 is passedthrough as coinciding with the first pulse 18 a of genlock signal 12.The DMX 512 data now passes into a buffer within the synchronizer of theinvention. This buffer differs from that described in the firstembodiment in that it accumulates multiple pending DMX 512 data framesawaiting the arrival of the next genlock pulse 18. Thus, frame 2 isaccumulated in the buffer and is output on receipt of the next genlockpulse 18 b. DMX 512 frame 3 is next accumulated within the buffer,however frame 4 arrives before the next genlock pulse is seen. Thus, thebuffer additionally accumulates frame 4 and creates a new, interpolated,frame from the data contained in both frame 3 and frame 4. The newlycreated interpolated frame is then output on receipt of the next genlockpulse 18 c. The system proceeds in this manner and outputs DMX 512frames 1, 2, 3+4, 5+6, 7+8, 9, and 10+11 synchronized with genlockpulses 18 a-18 g. The ‘+’ symbol in this case indicates a combinationand/or interpolation of the relevant frames. Such combination andinterpolation may proceed in a pre-determined manner that may differwith different lighting instruments. For example, a simple averagedvalue for each lighting channel may be appropriate for lightingintensity information, while a more complex combination algorithm may beneeded for color, position, or other lighting related data. Theinvention may provide any interpolation or combination algorithms asappropriate. While the example shows interpolation of two frames inother embodiments there may be more or less frames that requireinterpolation depending on how many DMX 512 frames occur between any twovideo frames. In some embodiments the number frames may be consistent inother embodiments the number of frames to be interpolated may not beconsistent.

FIG. 4 illustrates a timing diagram of a third embodiment of theinvention. The timing diagram presents the same situation as FIG. 1where the DMX 512 frame rate is greater than that of the video genlocksignal. In this embodiment the data reduction is achieved through thefull processing and re-timing of DMX 512 data frames instead of eitherdiscarding frames or performing simple interpolation/ combination on twoframes at a time. This embodiment is more complex than those illustratedin FIGS. 2 and 3, the synchronizer of the invention may decode the DMX512 data and re-generate it 22 using the genlock pulses 18 a-18 g as atiming reference. The synchronizer may be configured to have knowledgeof the types of lighting instruments connected to the DMX 512 datastream, and will re-generate data accordingly. In the exampleillustrated DMX 512 frames 1 to 12 are processed and re-timed to beoutput as DMX 512 frames 23 a-23 g to correspond with genlock pulses 18a-18 g.

FIG. 5 illustrates a timing diagram for a fourth embodiment of theinvention. In this embodiment the synchronizer of the invention has beenincorporated within the lighting control system directly. This may berepresented as hardware and/or software within, for example, a lightingcontrol desk, media server or intelligent lighting node 24.Synchronization of the DMX 512 output to the genlock signal 12 may nowhappen before any DMX 512 signal is generated. The lighting controlsystem itself will generate DMX 512 lighting frames 25 a-25 g using thegenlock pulses 18 a-18 g as the timing reference.

In yet further embodiments of the invention the describedsynchronization technique can be applied to multiple separate datastreams of DMX 512. (Different data streams of DMX 512 are oftenreferred to as universes). If each data stream/universe is independentlyand individually synchronized to the same video signal then the DMX 512data streams will also be synchronized with each other. The use ofmultiple DMX 512 data streams in a single large show is commonplace and,with the advent of fast reacting LED based luminaires, timingdifferences between the different DMX 512 data streams can be apparentto the viewers, with slight delays showing up between the lightingchanges on one part of a stage compared to another art of the same stagethat is running a separate DMX 512 data stream. If all data streamsoriginate from the same lighting control console then some of thissynchronization can happen within that consoled, however if, as isbecoming common, there are multiple lighting controllers, nodes,computers and other devices generating DMX 512 data streams then thereis no existing means to synchronize those data streams.

In this disclosure the invention the synchronizing signal has beendescribed as originating from a video signal. This is because thesynchronizing with video is one of the primary drivers for the need forthe invention. However, the invention is not so limited and othersignals could be used as the synchronizing source. For example,synchronization timing could be derived from a master DMX 512 datastream, from time code (such as SMPTE VITC) embedded in video, audio orlighting signals, from the mains power signal, from time code derivedfrom Ethernet or other networking protocols, from Artnet, ACN, RDM orany other time code or heart-beat signal that are well known in the art.

Although this disclosure has discussed the invention in particularexemplary embodiments, the invention is not so limited and furtherembodiments of the invention may achieve comparable results where thelighting data frame is synchronized to the video data frame.

While the disclosure has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments may be devised whichdo not depart from the scope of the disclosure as disclosed herein. Thedisclosure has been described in detail, it should be understood thatvarious changes, substitutions and alterations can be made heretowithout departing from the spirit and scope of the disclosure.

What is claimed is:
 1. A lighting control system comprising: a light emitting device that utilizes a frame based video signal; a timed control signal for controlling light output; and a synchronizer that synchronizes the timing of the control signals output to the frame rate of the video signal.
 2. The lighting control system of claim 1 further comprising: a second timed control signal for controlling light output and the synchronizer synchronizes the timing of the second timed control signal with the first timed control signal to the frame rate of the video signal.
 3. The lighting control system of claim 1 where time timed control signal for controlling light output is a plurality of timed control signals and all of the plurality are synchronized with the frame rate of the video signal.
 4. A DMX 512 lighting control system further with a synchronizer for receiving a synchronizing signal and synchronizing the DMX output(s) to synchronized in accordance with the synchronizing signal. 